This was my take-away as well. This is cool and all, but if your mapping problem can be entirely solved declaratively like this I don't know if you actually had

This was my take-away as well. This is cool and all, but if your mapping problem can be entirely solved declaratively like this I don't know if you actually had all that tough of a problem in the first place. Almost every data translation nightmare I've been sucked into involved some pretty sophisticated business logic, and any declarative language that has the sufficient power to handle it inevitably becomes more complicated to write and maintain than a turing-complete, plain old programming language.